This invention relates generally to air suction or aspiration devices of gas-turbine engines mounted on aircraft. More particularly, the invention relates to an air aspiration device affording stable air aspiration through the air intake duct and improvement of the air aspiration efficiency.
During normal flight of an aircraft powered by a gas-turbine engine, the air aspirated or drawn into its engine flows smoothly along fair streamlines without any turbulence. However, when the aircraft assumes a flight state such as a spin in which it maneuvers forward with a large angle of attack, or angle of incidence (which may reach a value as high as 50 degrees in some cases), the angle of the incident air flow relative to the centerine of the air intake duct becomes large until, ultimately, the air stream which has entered the air intake duct separates away therefrom from a point near the lower leading edge thereof. The flow of the aspirated air thus becomes greatly turbulent, and the air aspiration efficiency drops.
When the aircraft assumes the above described condition, as described hereinafter with reference to illustrations, its engine, or engines, will operate defectively and eventually stop, and flight thereafter will become difficult. Thus, the above described condition is very dangerous.
Consequently, the only recourse for avoiding this danger has heretofore been, ordinarily, to resort to a regulatory limitation such as banning or restricting maneuvers entailing large angles of attack such as spinning. This measure results in a great reduction in the performance value of the airframes of aircraft such as fighter planes and trainers therefor which are required to possess high degrees of maneuverability.
In order to remove this limitation, some fighter planes are provided with means such as a movable leading edge of each air intake duct, the direction of the leading edge being adjusted in accordance with the flight state. However, for deriving full effectiveness from such means, a complicated and expensive movement control mechanism is necessary, and, moreover, the weight of the air intake structure increases. Thus, this measure is not desirable.